CVE-2023-1998

Spectre v2 SMT mitigations problem in Linux kernel

Published Apr 21, 2023 CVSS 3.1 · 5.6 Medium EPSS 1.4% KEV · Not listed
Description
The Linux kernel allows userspace processes to enable mitigations by calling prctl with PR_SET_SPECULATION_CTRL which disables the speculation feature as well as by using seccomp. We had noticed that on VMs of at least one major cloud provider, the kernel still left the victim process exposed to attacks in some cases even after enabling the spectre-BTI mitigation with prctl. The same behavior can be observed on a bare-metal machine when forcing the mitigation to IBRS on boot command line.

This happened because when plain IBRS was enabled (not enhanced IBRS), the kernel had some logic that determined that STIBP was not needed. The IBRS bit implicitly protects against cross-thread branch target injection. However, with legacy IBRS, the IBRS bit was cleared on returning to userspace, due to performance reasons, which disabled the implicit STIBP and left userspace threads vulnerable to cross-thread branch target injection against which STIBP protects.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-3403-1 linux security update
Debian DLA Debian DLA DLA-3404-1 linux-5.10 security update
EUVD EUVD EUVD-2023-24178 The Linux kernel allows userspace processes to enable mitigations by calling prctl with PR_SET_SPECULATION_CTRL which disables the speculation feature as well as by using seccomp. We had noticed that on VMs of at least one major cloud provider, the kernel still left the victim process exposed to attacks in some cases even after enabling the spectre-BTI mitigation with prctl. The same behavior can be observed on a bare-metal machine when forcing the mitigation to IBRS on boot command line. This happened because when plain IBRS was enabled (not enhanced IBRS), the kernel had some logic that determined that STIBP was not needed. The IBRS bit implicitly protects against cross-thread branch target injection. However, with legacy IBRS, the IBRS bit was cleared on returning to userspace, due to performance reasons, which disabled the implicit STIBP and left userspace threads vulnerable to cross-thread branch target injection against which STIBP protects.
Ubuntu USN Ubuntu USN USN-6033-1 Linux kernel (OEM) vulnerabilities
Ubuntu USN Ubuntu USN USN-6171-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-6172-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-6185-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-6187-1 Linux kernel (IBM) vulnerabilities
Ubuntu USN Ubuntu USN USN-6207-1 Linux kernel (Intel IoTG) vulnerabilities
Ubuntu USN Ubuntu USN USN-6222-1 Linux kernel (Xilinx ZynqMP) vulnerabilities
Ubuntu USN Ubuntu USN USN-6223-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-6256-1 Linux kernel (IoT) vulnerabilities
Ubuntu USN Ubuntu USN USN-6739-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-6740-1 Linux kernel vulnerabilities
History
Type Values Removed Values Added
Description The Linux kernel allows userspace processes to enable mitigations by calling prctl with PR_SET_SPECULATION_CTRL which disables the speculation feature as well as by using seccomp. We had noticed that on VMs of at least one major cloud provider, the kernel still left the victim process exposed to attacks in some cases even after enabling the spectre-BTI mitigation with prctl. The same behavior can be observed on a bare-metal machine when forcing the mitigation to IBRS on boot command line. This happened because when plain IBRS was enabled (not enhanced IBRS), the kernel had some logic that determined that STIBP was not needed. The IBRS bit implicitly protects against cross-thread branch target injection. However, with legacy IBRS, the IBRS bit was cleared on returning to userspace, due to performance reasons, which disabled the implicit STIBP and left userspace threads vulnerable to cross-thread branch target injection against which STIBP protects. The Linux kernel allows userspace processes to enable mitigations by calling prctl with PR_SET_SPECULATION_CTRL which disables the speculation feature as well as by using seccomp. We had noticed that on VMs of at least one major cloud provider, the kernel still left the victim process exposed to attacks in some cases even after enabling the spectre-BTI mitigation with prctl. The same behavior can be observed on a bare-metal machine when forcing the mitigation to IBRS on boot command line. This happened because when plain IBRS was enabled (not enhanced IBRS), the kernel had some logic that determined that STIBP was not needed. The IBRS bit implicitly protects against cross-thread branch target injection. However, with legacy IBRS, the IBRS bit was cleared on returning to userspace, due to performance reasons, which disabled the implicit STIBP and left userspace threads vulnerable to cross-thread branch target injection against which STIBP protects.
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Sources

Status
PUBLISHED
Assigner
Google
Published
Updated
Feb 13, 2025, 4:39 PM
Reserved
Apr 12, 2023, 9:38 AM
Status
Modified
Published
Apr 21, 2023, 3:15 PM
Modified
Jun 17, 2026, 5:29 AM
Severity
Moderate
Public date
Apr 12, 2023, 12:00 AM